Learning reflects the ability of animals to constantly update their behavioral responses with new information obtained from their environments. Habituation is a simple form of learning, and allows animals to cease responding to repeated and non-threatening visual, tactile or acoustic stimuli. In humans, habituation learning is disrupted in schizophrenia and attention deficit disorders. Yet despite its importance, the genetic programs and molecular mechanisms that govern the assembly and function of the neuronal circuits critical for habituation are not well understood. Larval zebrafish exhibit numerous complex behaviors relevant to the study of neuropsychiatric disorders, including prepulse inhibition and startle habituation. The Granato lab has developed an automated, high-throughput assay that measures startle habituation, and has conducted a small molecule screen that revealed that the neuro-pharmacological substrates for startle habituation are conserved between zebrafish and humans. Furthermore, the Granato lab has conducted the first forward genetic screen for genes critical for vertebrate startle habituation. This screen has identified eight mutants with deficits in habituation learning, and the lab has already identified the molecular lesions for three of these mutants. One of the mutant phenotypes is caused by a presumptive null mutation in pregnancy associated plasma protein a (papp-a), a vertebrate specific gene previously not implicated in habituation learning. Although papp-a is expressed in the mammalian brain, its role in nervous system development or function is unknown. Here, I propose to identify where and when this gene acts to regulate habituation (Aim 1). Since papp-a plays a well-documented role in insulin-like growth factor (IGF) signaling, I will determine whether papp-a's regulation of habituation is executed through the canonical IGF signaling pathway or through a novel, IGF signaling independent pathway (Aim 2). To identify additional regulators critical for startle habituation, I will apply whole genome sequencing to identify the genes mutated in two additional habituation mutants isolated in the screen. Combined, these experiments will characterize the function of the papp-a gene in regulating habituation behaviors and identify novel genes required for the regulation of habituation behaviors in a vertebrate context. These studies will illuminate the cellular and molecular mechanisms required for the development and function of cells mediating startle habituation. Given the importance of startle habituation and learning processes for nervous system function in healthy and disease states, the proposed studies are of high relevance to both basic science and human health.